The present invention relates to improvements in reinforcing sheet metal ducts. The sheet metal which is commonly used in duct formation for handling, typically airflows, can come in various gauges or thicknesses. Good engineering practices dictate the use of various construction details during the assembly of the duct from the sheet metal material in order to provide the resulting duct with sufficient strength to withstand the forces to be exerted in its lifetime. These engineering practices are embodied in standards established by ASHRAE and SMACNA.
Among those standards are requirements that the sheet metal be reinforced in some circumstances. A common reinforcement method is called cross-breaking, in which a sheet has two intersecting creases formed in it, resulting in the appearance of an X-shaped dent.
A newer reinforcement technique is the formation of bead in the duct, in the form of a single corrugation as an outward bend in the wall of the duct extending around the periphery of the duct. These may be spaced at prescribed distances along the length of the duct. Machinery commonly available in sheet metal shops is now used for the formation of these beads at the desired locations. Where even a higher level of reinforcement is required by ASHRAE or SMACNA, it is conventional to attach angle irons to the walls of the duct. The attachment of the angle irons is a time-consuming and tedious process. First, the prescribed location of the angle iron on the length of the duct must be ascertained and a line drawn on the duct corresponding to the desired placement. Typically, the angle irons are predrilled with holes, but if not, the angle irons need to be drilled with holes to receive bolts. Corresponding holes must be drilled in the duct. Then, a nut and bolt are used to fasten the angle iron through the aligned holes of the angle iron and duct. Often, this is a two-man process, especially for larger cross section ducts, which are those most likely to need reinforcement. Thus, the labor expense of reinforcing ducts this way is great. Also, the contractor needs to keep angle irons in inventory, adding to his inventory expense. There is a need in the art for a less expensive way to achieve reinforcement of ducts.